docs: def build_one(self, package_dir, filename, source_map=False):
          """Builds one Sass/SCSS file.
  
          :param package_dir: the path of package directory
          :type package_dir: :class:`str`, :class:`basestring`
          :param filename: the filename of Sass/SCSS source to compile
          :type filename: :class:`str`, :class:`basestring`
          :param source_map: whether to use source maps.  if :const:`True`
                             it also write a source map to a ``filename``
                             followed by :file:`.map` suffix.
                             default is :const:`False`
          :type source_map: :class:`bool`
          :returns: the filename of compiled CSS
          :rtype: :class:`str`, :class:`basestring`
  
          .. versionadded:: 0.4.0
             Added optional ``source_map`` parameter.
  
          """
          sass_filename, css_filename = self.resolve_filename(
              package_dir, filename,
          )
          root_path = os.path.join(package_dir, self.sass_path)
          css_path = os.path.join(package_dir, self.css_path, css_filename)
          if source_map:
              source_map_path = css_filename + '.map'
              css, source_map = compile(
                  filename=sass_filename,
                  include_paths=[root_path],
                  source_map_filename=source_map_path,  # FIXME
                  output_filename_hint=css_path,
              )
          else:
              css = compile(filename=sass_filename, include_paths=[root_path])
              source_map_path = None
              source_map = None
          css_folder = os.path.dirname(css_path)
          if not os.path.exists(css_folder):
              os.makedirs(css_folder)
          with io.open(css_path, 'w', encoding='utf-8', newline='') as f:
              f.write(css)
          if source_map:
              # Source maps are JSON, and JSON has to be UTF-8 encoded
              with io.open(
                  source_map_path, 'w', encoding='utf-8', newline='',
              ) as f:
                  f.write(source_map)
          return css_filename